I am interested in buying an old iMac 3G, love the colors and how they look. Not a problem because you can find them anywhere, but what would be a good model to get and upgrade as a project, I do want an DVD drive if possible. 

If you look hard enough I'm sure you can find a processor upgrade one of them.
Please, post pictures. Many of us will put them up on the bulletin board next to Jeebus and Machu Picchu. Great idea!I have a blueberry iMac that I plan on ripping everything out, putting in a new screen, get some glass cut to make it look cathode like and put a modern computer in it, or I might just take the shape of an iMac G3 and extrapolate it to 20"+ and put a full computer in it
Slot loading G3 iMacs don't have processor upgrades. The CPU is soldered on to the logic board. The older tray loading G3's do have an upgradable processor, but the fastest is only 333Mhz.
Please, post pictures. Many of us will put them up on the bulletin board next to Jeebus and Machu Picchu. Great idea!